I don't know whether it's available outside the U.S., but I second AR1911's suggestion of Evapo-Rust. It really works wonders! (I have no affiliation - just a satisfied customer.)
In the U.S., some auto parts stores have it, and it's available through amazon.com and eBay. Highly recommended!
I should mention that I've used vinegar, molasses, and electrolysis, among other approaches, and Evapo-Rust is by far the fastest and easiest method. The results are amazing, and it only affects the rust, not the base metal.
Note that, for best results and longest life of the solution, the parts should be degreased before using Evapo-Rust, which can be re-used repeatedly.
-Chris